1. Field of the Invention
The present invention relates to a sheet-workpiece bending machine, and more particularly to a sheet workpiece bending machine capable of performing a precise bending operation in a sheet workpiece.
2. Description of the Prior Art
In sheet-metal bending presses used as sheet workpiece bending machines, the punch and the die, as upper and lower bending tools, are supported by beams as an apron. The beams are usually narrow but very deep so that they can resist deflection under the bending stress which, in machines of a certain length, is exerted by two fluidic cylinders situated at the ends of the movable beam. The flexural strength of the beams is very important since their deflection causes a difference in the distance between the punch and the die in the central section compared with the side sections of the beam. Even if it is limited, this deflection causes the sheet metal to be bent at an angle which is not constant along the length of the bend.
In very long bending presses, for bending pieces of sheet metal several meters long, the depths of the beam reach high values of the order of two meters or more. In fact, for a given central deflection, as the length of the beam increases, its moment of inertia must increase as the cube of the length of the beam.
This means that the machine is very high. Amongst other things, in a vertical machine, that is, of the most usual type, the considerable depth of the lower beam involves the need to form a well in the workshop floor to house the bulk of this beam and thus keep the working plane in an ergonomic position.